Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use either thermal ink jet technology or piezoelectric technology. Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored as they can use a wider variety of inks and reduce or eliminate problems with kogation.
Piezoelectric ink jet print heads typically include a flexible diaphragm and an array of piezoelectric elements (i.e., transducers or PZT's) attached to the diaphragm. When a voltage is applied to a piezoelectric element, typically through electrical connection with an electrode electrically coupled to a voltage source, the piezoelectric element bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
Increasing the printing resolution of an ink jet printer employing piezoelectric ink jet technology is a goal of design engineers. Increasing the jet density of the piezoelectric ink jet print head can increase printing resolution. One way to increase the jet density is to eliminate manifolds which are internal to a jet stack. With this design, it is preferable to have a single port through the back of the jet stack for each jet. The port functions as a pathway for the transfer of ink from the reservoir to each jet chamber. Because of the large number of jets in a high density print head, the large number of ports, one for each jet, must pass vertically through the diaphragm and between the piezoelectric elements.
Processes for forming a jet stack can include the formation of an interstitial layer from a polymer material between each piezoelectric element and, in some processes, over the top of each piezoelectric element. If the interstitial layer is dispensed over the top of the each piezoelectric element, it is removed to expose the conductive piezoelectric element. Next, a patterned standoff layer having openings therein can be applied to the interstitial layer, where the openings expose the top of each piezoelectric element. A quantity (i.e., a microdrop) of conductor such as conductive epoxy, conductive paste, or another conductive material is dispensed individually on the top of each piezoelectric element. Electrodes of a flexible printed circuit (i.e., a flex circuit) or a printed circuit board (PCB) are placed in contact with each conductor microdrop to facilitate electrical communication between each piezoelectric element and the electrodes of the flex circuit or PCB. The standoff layer functions to contain the flow of the conductive microdrops to the desired locations on top of the piezoelectric elements, and also functions as an adhesive between the interstitial layer and the flex circuit or PCB.
During the formation of the jet stack, it is important to keep jet stack layers such as the interstitial layer uniformly thick across the surface of the jet stack. Thickness conformity is advantageous as it can help mitigate issues caused by jet stack thickness variation, PZT thickness variation, or attachment thickness variation. Forming the interstitial layer to a uniform thickness decreases problems such as poor ink communication within the completed printhead, and can reduce the incidence of ink leaks within the printhead.